Search radar systems of the type considered here employ a rotating fan beam to locate targets in azimuth and elevation. In order to obtain maximum range and accuracy, it is important to stabilize the beam in its spacial orientation.
Radar antennas generally utilize a primary focusing structure which radiates energy onto a secondary focusing structure. The primary focusing structure defines the general beam-shape and acts as a source of energy illuminating the secondary focusing structure. The secondary focusing structure in turn collimates the incident energy and forms a beam which is an image of the source at infinity.
The primary focusing structure is generally small and lightweight. In contrast, the secondary focusing structure typically is rather large and massive.
Search radar antennas are often placed on a moveable vehicle such as an airplane, ship or ground vehicle. The vehicle will generally be non-stationary, and in general will be given to roll, pitch, and yaw. This motion must be compensated for in order to stabilize the beam.
Prior methods of stabilization involved mounting of the entire antenna structure on a stabilized platform. Unfortunately, stabilization of large antennas in this manner not only adds undesirable additional weight to the carrying vehicle and requires a high-power system to manipulate the stabilizing platform, but results in poor antenna-stabilization bandwidth characteristics.